Mitochondrial membrane potential disruption pattern in human sperm

BACKGROUND Loss of mitochondrial membrane potential (ΔΨm) in spermatozoa is correlated with high levels of reactive oxygen species in semen, abnormal spermiogram parameters, and low success rates of IVF. In somatic cells, the loss of ΔΨm is primarily associated with several mechanisms of cell death, mainly the activation of caspases. The impact of mitochondrial dysfunction on sperm function is still not fully elucidated, although disruption of ΔΨm and activation of caspases are processes thoroughly studied in human ejaculates. Disruption of ΔΨm in sperm can be externally triggered by the antineoplastic agent betulinic acid (BA). In this study, we determined whether caspase activation is necessary for the BA-induced disruption of ΔΨm in human sperm. METHODS Viable and highly motile sperm cells were selected through a swim-up process and incubated with 90 µg/ml BA. To elucidate the caspase dependency of BA-triggered disruption of ΔΨm, we used the pan-caspase inhibitor zVAD-fmk and the caspase-3/7 inhibitor DEVD-cho. RESULTS Exposing highly motile sperm to BA caused a specific disruption of ΔΨm (P < 0.001 versus control) and a corresponding increase in caspase-3/7 activity (P < 0.001 versus control). Pre-incubation of the sperm with zVAD-fmk or DEVD-cho only partially inhibited BA-induced loss of ΔΨm (P < 0.05 versus control). CONCLUSION We found that caspases directly participate in the loss of ΔΨm caused by BA in human sperm cells. However, caspase-independent pathways may also be present.